1. Field of the Invention
The present invention relates to sustained release drug delivery systems for use in the eye. More specifically, this invention relates to the use of high molecular weight cationic polymers having bioadhesive properties for the sustained release of ophthalmic preparations.
2. Description of Related Art
Simple aqueous drug dosage forms such as eye drops are widely used for the treatment of ophthalmic disorders. In many cases, these dosage forms are disadvantageous because the applied drug is rapidly removed from the eye through a mechanism of drug dilution and drug elimination caused by the continuous turnover of the tear fluid.
Sustained release drug systems which remain present on the eye for prolonged periods of time have been developed in the past based on the individual pharmacokinetics of the drugs to be released. These systems may include, for example, microscopical implants containing a semipermeable membrane which acts as a diffusion barrier and is responsible for sustained release of the principal active ingredient.
A significant drawback of the above described systems is the fact that these systems must be mechanically placed on the eye and subsequently, after completion of drug release, must be mechanically removed. The mechanical manipulations required with this type of system render the system unacceptable to many patients. There is therefore a need for a more convenient sustained release drug delivery system suitable for ophthalmic use.
Prior developments in connection with the use of high molecular weight polymers in ophthalmic dosage forms are described in U.S. Pat. Nos. 4,271,143 and 4,407,792. These patents relate to an aqueous dispersion of an ophthalmic drug and a high molecular weight polymer which forms a highly viscous gel and can be used to prolong the duration of activity of the ophthalmic drug when the gel is applied into the conjuctival sac of the eye. The high molecular weight polymers described in these patents include carboxyvinyl polymers (e.g., carboxypolymethylene) and ethylene maleic anhydride polymer.